To improve machining precision, automatic control machine tools use a workpiece measuring instrument to measure the dimensions of a roughly machined workpiece to correct the amount by which a tool is fed during finish machining on the basis of measurements. For example, the Unexamined Japanese Patent Application Publication (Tokkai) 2004-34187 describes an example in which the machine tool is a lathe having, instead of tools, workpiece measuring instruments mounted on some of a plurality of tool stations of a tool stand comprising a turret.
In the Unexamined Japanese Patent Application Publication (Tokkai) 2004-34187, the workpiece measuring instruments are mounted on the tool stand and located near a machining position during workpiece machining. Consequently, chips resulting from cutting may adhere to the workpiece measuring instruments to affect their detection precision. Machining vibration may also propagate to the workpiece measuring instruments, which may thus fail. The workpiece measuring instruments located near the machining position are also likely to be affected by cutting heat, and the workpiece measuring instruments may become hot and defective or have their functions degraded.
An object of the present invention is to provide a machine tool with a workpiece measuring instrument which prevents the workpiece measuring instrument from being affected by chips or cutting heat during non-machining, while enabling a workpiece to be measured near a machining position. Another object of the present invention is to provide a simplified means for switching a position of the workpiece measuring instrument.